1. Field of the Invention
The present invention relates to a method of manufacturing an electron source with an electron emitting element, a method of manufacturing an image forming apparatus, and apparatuses for manufacturing these electron source and image forming apparatus.
2. Related Background Art
Two types of electron emitting elements are known as roughly classified into a thermal electron emitting element and a cold cathode electron emitting element. The types of a cold cathode electron emitting element include a field emission type (hereinafter called an FE type, a metal/insulator/metal type (hereinafter called an MIM type), a surface conduction type electron emission type, and the like.
Examples of the FE type are disclosed in xe2x80x9cField emissionxe2x80x9d, by W. P. Dyke and W. W. Dolan, Advance in Electron Physics, 8, 89 (1956), xe2x80x9cPhysical properties of thin-film field emission cathodes with molybdenum conesxe2x80x9d, by C. A. Spindt, J. Appl. Phys., 47, 5248 (1976) and other papers.
Examples of the MIM type are disclosed in xe2x80x9cOperation of Tunnel-Emission Devicesxe2x80x9d, by C. A. Mead, J. Appl., Phys., 32, 646 (1961) and other papers.
Examples of the surface conduction type electron emission element are disclosed in Recio Eng. Electron Phys., by M. I. Elinson, 10, 1290 (1965) and other papers.
The surface conduction type electron emitting element utilizes the phenomenon that when current is flowed in a thin film having a small area formed on a substrate in parallel to the film surface, electron emission occurs. Reported thin films for a surface conduction type electron emitting element include an SnO2 thin film by Elinson, an Au thin film (xe2x80x9cThin Solid Filmsxe2x80x9d, 9, 317 (1972)), an In2O3/SnO2 thin film (xe2x80x9cIEEE Trans. ED conf.xe2x80x9d, by M. Hartwell and C. G. Fonstad, 519 (1975)), a carbon thin film (xe2x80x9cVacuumxe2x80x9d, by Hisashi ARAKI, et al. vol. 26, No. 1. p. 22 (1983)), and the like.
As a typical example of a surface conduction type electron emitting element, the structure of an element proposed by M. Hartwell is schematically shown in FIG. 16. In FIG. 16, reference numeral 1 represents a substrate, and reference numerals 2 and 3 represent element electrodes. Reference numeral 4 represents a conductive thin film which is made of a metal oxide thin film having an H-character shape formed by sputtering. An electron emitting area 5 is formed in the conductive thin film by a power conduction process called a power conduction forming process to be described later. A distance L1 between the element electrodes is 0.5 to 1 mm, and a width W of the conductive thin film 4 is 0.1 mm.
Conventionally, the electron emitting area 5 of a surface conduction type electron emitting element is generally formed in the conductive thin film 4 by the power conduction process called the power conduction forming process, before electron emission is enabled. With the power conduction forming process, a d.c. voltage or a voltage rising very gently, e.g., at about 1 V/min is applied across the electrodes of the conductive thin film 4 to locally break, deform, or decompose to form the electron emitting area 5 having a high electric resistance.
Cracks or the like are formed in the electron emitting area 5 of the conductive thin film 4 and electrons are emitted from the cracks and nearby areas. When a voltage is applied to the conductive thin film 4 of a surface conduction type electron emitting element subjected to the power conduction forming process and current is flowed therethrough, electrons are emitted from the electron emitting area 5.
Since the structure of a surface conduction type electron emitting element is simple and the manufacture thereof is easy, a number of elements can be disposed in a large area. By utilizing this advantageous feature, various applications have been studied. For example, the surface conduction type electron emitting element may be used for a charged beam source, a display device, and the like. As will be later described, as an example of disposing a number of surface conduction type electron emitting elements, an electron source is known which has a number of rows disposed in parallel each having a plurality of surface conduction type electron emitting elements each having both terminals being connected by wiring patterns (also called common wiring patterns) (e.g., JP-A-64-031332, JP-A-1-283749, JP-A-2-257552, or the like).
A flat panel type display device using liquid crystal has recently been prevailed as an image forming apparatus in place of a CRT. However, since the flat panel type display device using liquid crystal is not of a self-light emission type so that a back light becomes necessary. Developments on a display device of a self-light emission type have long been desired. As a self-light emission type display device, an image forming apparatus is known which is a combination of an electron source with a number of surface conduction type electron emitting elements and a fluorescent body capable of radiating visible rays upon application of electrons emitted from the electron source (e.g., U.S. Pat. No. 5,066,883).
The present applicant has proposed a surface conduction type electron emitting element having the structure schematically shown in FIGS. 2A and 2B and an image forming apparatus using such electron emitting elements. The details of the structure of the electron emitting element and image forming apparatus and the manufacture methods thereof are described, for example, in JP-A-7-235255, JP-A-7-235275, JP-A-8-171849, and the like.
This surface conduction type electron emitting element is constituted of a pair of element electrodes 2 and 3 facing each other on a substrate 1, and a conductive film 4 having an electron emitting area 5 connected between the element electrodes 2 and 3. The electron emitting area 5 is a high electric resistance area formed by locally breaking, deforming or decomposing the conductive film 4. Cracks or the like are formed in the electron emitting area 5 of the conductive thin film 4. Electrons are emitted from the nearby area of the cracks. The electron emitting area and its nearby area is formed with a deposit film containing at least carbon.
The conductive film is preferably made of conductive fine particles in order to form the electron emitting area of a proper performance by the power conduction process (forming process) to be later described.
The manufacture process will be described briefly with reference to FIGS. 4A to 4C.
First, element electrode 2 and 3 are formed on a substrate 1 by suitable methods such as printing, vacuum deposition, and photolithography techniques (FIG. 4A).
Next, a conductive film 4 is formed. The conductive film 4 may be deposited by vacuum deposition, sputtering or the like and patterned, or it may be formed by coating liquid which contains source material of the conductive film.
For example, solution of metal organic compound is coated and thermally decomposed to form a metal or metal oxide. In this case, a fine particle film can be formed under the proper film forming conditions.
After the conductive film is formed, it may be patterned to a desired shape. Alternatively, as described in JP-A-9-69334, source material liquid may be coated by an ink jet apparatus or the like to make it have a desired shape, and thereafter it is thermally decomposed to form a conductive film having a desired shape without using a patterning process.
Next, an electron emitting area 5 is formed. This area may be formed by applying a voltage across the element electrodes 2 and 3 and flowing current through the conductive film to locally deform or decompose the conductive film (power conduction forming process). The voltage is preferably a pulse voltage. Waveforms of the pulse voltage may have a constant peak value as shown in FIG. 5A, a peak value gradually increasing with time as shown in FIG. 5B, or a combination of these. It is desired that while a forming pulse is not applied (during a period between pulses), a pulse having a sufficiently low peak value is inserted to measure a resistance value, and that when the resistance value of the electron emitting area increases sufficiently, e.g., when it exceeds 1 Mxcexa9, the pulse application is stopped.
For this process, generally, the electron emitting element is placed in a vacuum chamber which may be evacuated by an evacuator, into which oxidizing gas may be introduced, or into which reducing gas may be introduced. A proper state is selected in accordance with the conditions such as the material quality of the conductive film or the like.
Next, an activating process is performed. This process deposits material containing at least carbons near on the electron emitting area formed by the forming process, to thereby increase the amount of electrons to be emitted. Generally, this process of depositing material containing at least carbon is performed by placing an electron emitting element in a vacuum chamber, evacuating the inside of the chamber, and applying a pulse voltage across a pair of element electrodes to thereby decomposing and polymerizing organic material present in the vacuum at a low partial pressure. The organic material may be introduced directly into the vacuum chamber after it is evacuated, or it may be diffused into the vacuum chamber by using a proper apparatus such as an oil diffusing pump.
It is preferable to perform a stabilizing process after the activating process. This process is performed in order to sufficiently remove organic material molecules attached to the electron emitting element, its nearby area, and the inner wall of a vacuum housing of the electron emitting element, to thereby prevent material containing carbon from being thereafter deposited during the operation of the element and stabilize the characteristics of the element.
More specifically, for example, an electron emitting element is placed in a vacuum chamber (which may be the same chamber as used in the activating process), and the electron emitting element and vacuum chamber are heated while the vacuum chamber is evacuated by an oil-free evacuator such as an ion pump. This heating is performed in order to detach and sufficiently remove organic material molecules attached on the electron emitting element and on the inner wall of the vacuum chamber. At the same time, or after the heating is stopped, if a drive voltage is applied to the electron emitting element while the inside of the vacuum chamber is evacuated, the electron emission effect may be improved in some cases. Depending upon the kind of organic material introduced during the activating process, the electron emission effect may be improved by driving the electron emitting element in a high vacuum state of the vacuum chamber. The stabilizing process is therefore performed by a method most suitable for respective conditions.
A typical example of the operation characteristics of the surface conduction type electron emitting element manufactured by the above-described method is shown in the graph of FIG. 7. This graph shows a relation between a current (element current) If flowing through the element upon application of a voltage Vf and an emission current Ie. Ic is very small as compared to If so that they are shown by arbitrary scales which are both linear scales. As seen from FIG. 7, the emission current Ie is non-linear having a threshold value (Vth) relative to Vf. If Vf is Vth or smaller, Ie is substantially 0, whereas if Vf exceeds Vth, Ie rises abruptly. In the example shown in FIG. 7, similar to Ie, If has also a threshold value relative to Vf and monotonously increases (MI characteristics) above Vf equal to or higher than the threshold value. However, depending upon the manufacture processes and measurement conditions, If may have a voltage controlled type negative resistance (VCNR characteristics). If the element has the VCNR characteristics, If-Vf characteristics are not stable, and although Ie has the MI characteristics, the characteristics are not stable. The stable MI characteristics may be obtained by performing the stabilizing process as disclosed, for example, in JP-A-7-235275.
Since the relation between Vf and Ie is non-linear having a definite threshold value, it is possible to emit electrons from a desired one of a plurality of electron emitting elements disposed on a substrate in a matrix form and wired together. A simple matrix drive is therefore possible.
An image forming apparatus using an electron source constituted of electron emitting elements has the electron source and an image forming member housed in a vacuum housing made of glass or the like. This electron source can be formed basically by the same method as above. In this case, instead of using a vacuum chamber, the vacuum housing made of glass and containing the electron source with conductive films and the image forming member may be used for the forming, activating, and stabilizing processes by evacuating the inside of the vacuum housing. Since a specific vacuum chamber for manufacturing an image forming apparatus is not necessary, the apparatus can be manufactured with a simple manufacture system.
Such an image forming apparatus has a great number of electron emitting elements integrated together. Highly sophisticated techniques are therefore required to manufacture with high yield an electron source whose all electron emitting elements operate normally. If each process is performed by using the vacuum housing containing the electron source and a defective element is formed during the process, it is impossible to repair it. Therefore, in manufacturing a large type or high precision type image forming apparatus having a great number of electron emitting elements, it is advantageous in some cases to perform each process by using a large vacuum chamber and thereafter house the electron source and image forming member in a vacuum housing.
Depending upon respective conditions, one of the above-described two methods, or an intermediate method of performing some processes by using a vacuum chamber and performing the remaining processes by housing the electron source and image forming material in a vacuum housing.
As schematically shown in FIG. 13, an electron source wired in a ladder shape may be used to form an image forming apparatus such as schematically shown in FIG. 14. In this case, grid electrodes are provided for modulating the amount of electron rays reaching the image forming member.
JP-A-9-330654 discloses a process of activating surface conduction type electron emitting elements by using a mixture gas of organic material and carrier gas.
It is an object of the present invention to provide techniques regarding the manufacture of an electron source with an electron emitting element, capable of lowering a manufacture cost, shortening a manufacture time, and improving the characteristics of a manufactured electron emitting element.
According to one aspect of the present invention, a method of manufacturing an electron source with an electron emitting element is provided which comprises the steps of: depositing a deposit substance in an area including at least an area of the electron emitting element from which area electrons are emitted, wherein the depositing step is performed in an atmosphere of a gas containing at least a source material of the deposit substance, the gas having a mean free path allowing the gas to take a viscous flow state.
According to another aspect of the invention, a method of manufacturing an electron source with an electron emitting element is provided which comprises the steps of: depositing a deposit substance in an area including at least an area of the electron emitting element from which area electrons are emitted, wherein the depositing step is performed in an atmosphere of a gas containing at least a source material of the deposit substance, the gas atmosphere having a pressure of 1 Pa or higher.
In the first and second aspects of the invention, the deposit substance area from which electrons are emitted may be an area from which electrons can be emitted before the depositing step.
The gas may be a gas made of a source material of the deposit substance diluted with dilution gas such as inert gas.
The gas may be a gas containing a source material of the deposit substance, and a gas of nitrogen, helium, or argon.
The gas may be a gas containing carbon or carbon compound, and a gas of nitrogen, helium, or argon.
The depositing step may deposit the deposit substance by applying a voltage across the area from which electrons are emitted, under the atmosphere.
The area from which electrons are emitted may be near at a first gapped area between conductive materials facing each other, and the depositing step may deposit the deposit substance over the facing conductive materials to form a second gapped area narrower than the first gapped area.
The first and second aspects of the invention may further comprise a first gapped area forming step of forming the first gapped area. The first gapped area forming step may the first gapped area by supplying a power to the conductive film where the first gapped area is formed.
The first gapped area forming step may be performed at a pressure nearly equal to the pressure used for the depositing step.
The first gapped area forming step and the depositing step may be performed at an approximately atmospheric pressure.
In the first and second aspects of the invention, the first gapped area forming step may be performed in an inert gas, in an oxidizing gas or a mixture gas containing oxidizing gas, or in a reducing gas or a mixture gas containing reducing gas.
In the first and second aspects of the invention, the depositing step may be performed in a container capable of being evacuated into the atmosphere.
The container may be a product housing the electron emitting element therein, an envelope of an image forming apparatus to be described later, or a manufacture system including a chamber different from an electron source or a product such as an image forming apparatus using the electron source. In this case, a step after the depositing step is completed may be performed by using a container different from the container used during the depositing step.
The container used during the depositing step may be provided with means for diffusing the gas. The diffusing means may be a mesh.
The depositing step may be performed by introducing the gas into the container, or by flowing the gas through the container. A method of introducing or flowing the gas into or through the container may use positive introducing means such as propellers and pumps.
The depositing step may be performed in a container having an inlet port and an outlet port for the gas. During the depositing step, the gas drained from the container may be again introduced into the container. Means for again introducing the gas may be positive introducing means (circulating means) such as propellers and pumps. Before the gas is again introduced into the container, unnecessary substances may be reduced from the gas drained from the container.
After the depositing step, moisture in the gas may be reduced.
The electron emitting element is preferably a cold cathode electron emitting element. It may be used properly as a surface conduction type electron emitting element.
The invention is particularly effective for forming a number of electron emitting elements.
According to a third aspect of the invention, a method of manufacturing an image forming apparatus having an electron source and an image forming member for forming an image by using electrons radiated from the electron source is provided which comprises the step of integrating the image forming member with an electron source manufactured by the above-described manufacture method.
According to a fourth aspect of the invention, a manufacture apparatus for manufacturing an electron source with an electron emitting element is provided which comprises: a container capable of introducing a gas thereinto; and means for introducing the gas in the container, the gas containing at least a source material of a deposit substance deposited in an area at least including an area of the electron emitting element from which electrons are emitted, wherein the introducing means introduces the gas in a viscous flow state.
According to a fifth aspect of the invention, a manufacture apparatus for manufacturing an electron source with an electron emitting element is provided which comprises: a container capable of introducing a gas thereinto; and means for introducing the gas in the container, the gas containing at least a source material of a deposit substance deposited in an area at least including an area of the electron emitting element from which electrons are emitted, wherein the introducing means introduces the gas at 1 Pa or higher of the atmosphere in the container.
In the third to fourth aspects of the invention, the introducing means may be an inlet port and an outlet port mounted on the container, a gas source such as a bomb containing a gas or a source material of the gas such as liquid, or introducing pipes.
The manufacture apparatuses may further comprise circulating means for introducing the gas drained from the container again into the container, or pipe means for introducing the gas drained from the container again into the container. The manufacture apparatuses may further comprise means for removing moisture in the gas to be again introduced into the container.
The container may cover a member such as the substrate including at least the area where the deposit substance is formed.
The manufacture apparatuses may include transport means for transporting a member containing at least the area where the deposit substance is formed, into the container.